Wed·Jul 1, 2020Wednesday·July 1, 2020

1. 01*

   Shape phase transitions in odd-A Zr isotopes

   K. Nomura🇭🇷 · T. Nikšić🇭🇷 · D. Vretenar🇭🇷

   Spectroscopic properties that characterize shape phase transitions in neutron-rich odd-A Zr isotopes are investigated using the framework of nuclear density functional theory and particle-core coupling. The interacting-boson Hamiltonian of the even-even core nuclei, and the single-particle energies and occupation probabilities of the unpaired neutron are completely determined by deformation constrained self-consistent mean-field calculations based on the relativistic Hartree-Bogoliubov model with a choice of a universal energy density functional and pairing interaction. The triaxial $(\beta ,\gamma )$ deformation energy surfaces for even-even ${}^{94-102}$Zr indicates transition from triaxial or $\gamma$-soft (${}^{94,96}$Zr) to prolate (${}^{98}$Zr), and triaxial (${}^{100,102}$Zr) shapes. The corresponding low-energy excitation spectra of the odd-A Zr isotopes are in very good agreement with recent experimental results. Consistent with the structural evolution of the neighboring even-even Zr nuclei, the state-dependent effective deformations and their fluctuations in the odd-A isotopes indicate a pronounced discontinuity around the transitional nucleus ${}^{99}$Zr.

   ↳ nucl-thnucl-exPRC(2020)·18 citations
2. 02*

   Revisiting the hypertriton lifetime puzzle

   A. Pérez-Obiol🇯🇵 · D. Gazda🇨🇿 · E. Friedman🇮🇱 · A. Gal🇮🇱

   Conflicting values of the hypertriton (${}_{\Lambda }^3$H) lifetime were extracted in recent relativistic heavy-ion collision experiments. The ALICE Collaboration's reported ${}_{\Lambda }^3$H lifetime $\tau {(}_{\Lambda }^3$H) is compatible within measurement uncertainties with the free $\Lambda$ lifetime ${\tau }_{\Lambda }$, as naively expected for a loosely bound $\Lambda$ hyperon in ${}_{\Lambda }^3$H, whereas STAR's reported range of $\tau {(}_{\Lambda }^3$H) values is considerably shorter: ${\tau }_{\mathrm{STAR}}{(}_{\Lambda }^3$H)$\sim$(0.4-0.7)${\tau }_{\Lambda }$. This ${}_{\Lambda }^3$H lifetime puzzle is revisited theoretically using ${}_{\Lambda }^3$H three-body wavefunctions generated in a chiral effective field theory approach to calculate the decay rate $\Gamma {(}_{\Lambda }^3$H${\to }^3$He$+{\pi }^{-}$). Significant but opposing contributions arise from $\Sigma NN$ admixtures in ${}_{\Lambda }^3$H and from ${\pi }^{-}$-${}^3$He final-state interaction. Evaluating the inclusive ${\pi }^{-}$ decay rate ${\Gamma }_{{\pi }^{-}}{(}_{\Lambda }^3$H) via a branching ratio $\Gamma {(}_{\Lambda }^3$H${\to }^3$He+${\pi }^{-})/{\Gamma }_{{\pi }^{-}}{(}_{\Lambda }^3$H) determined in helium bubble-chamber experiments, and adding ${\Gamma }_{{\pi }^0}{(}_{\Lambda }^3$H) through the $\Delta I=\frac{1}{2}$ rule, we derive $\tau {(}_{\Lambda }^3$H) assuming several different values of the $\Lambda$ separation energy $B_{\Lambda }{(}_{\Lambda }^3$H). It is concluded that each of ALICE and STAR reported $\tau {(}_{\Lambda }^3$H) intervals implies its own constraint on $B_{\Lambda }{(}_{\Lambda }^3$H): $B_{\Lambda }\lesssim 0.1$ MeV for ALICE, $B_{\Lambda }\gtrsim 0.2$ MeV for STAR.

   ↳ nucl-thhep-phnucl-exPLB(2020)·28 citations
3. 03*

   Updated MiniBooNE Neutrino Oscillation Results with Increased Data and New Background Studies

   MiniBooNE Collaboration · A. A. Aguilar-Arevalo · B. C. Brown · J. M. Conrad · R. Dharmapalan · A. Diaz · Z. Djurcic · D. A. Finley · R. Ford · G. T. Garvey · S. Gollapinni · A. Hourlier and 30 other authors

   The MiniBooNE experiment at Fermilab reports a total excess of $638.0\pm 132.8$ electron-like events ($4.8\sigma$) from a data sample corresponding to $18.75\times 10^{20}$ protons-on-target in neutrino mode, which is a 46\% increase in the data sample with respect to previously published results, and $11.27\times 10^{20}$ protons-on-target in antineutrino mode. The additional statistics allow several studies to address questions on the source of the excess. First, we provide two-dimensional plots in visible energy and cosine of the angle of the outgoing lepton, which can provide valuable input to models for the event excess. Second, we test whether the excess may arise from photons that enter the detector from external events or photons exiting the detector from ${\pi }^0$ decays in two model independent ways. Beam timing information shows that almost all of the excess is in time with neutrinos that interact in the detector. The radius distribution shows that the excess is distributed throughout the volume, while tighter cuts on the fiducal volume increase the significance of the excess. We conclude that models of the event excess based on entering and exiting photons are disfavored.

   ↳ hep-exhep-phnucl-exPRD(2021)·351 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.